Process of making an integrated circuit chip composite including parylene coated wire

ABSTRACT

A composite containing an integrated circuit chip having conductive site thereon and electrically conductive leads that are interconnected to the conductive site by electrically conductive wire; wherein the wire is coated with a dielectric material. Also, a method for fabricating the composite is provided.

This is a divisional application of Ser. No. 07/988,849, filed on Dec.10, 1992.

DESCRIPTION

1. Technical Field

The present invention is concerned with an integrated circuit chippackage and especially to providing improved interconnection betweenelectrically conductive sites thereon and electrically conductive leads.In addition, the present invention is concerned with a method forfabricating such a composite.

2. Background Art

In the fabrication of what is referred to as plastic flat pack packages,the electrically conductive sites or pads on an integrated circuit chipare connected to the electrically conductive leads by using a relativelythin wire, typically a gold wire. During molding to encapsulate thecomposite with a dielectric material, there is a tendency to causedistortion of the wires, thereby resulting in short circuiting. In orderto avoid this short circuiting, relatively short wires (e.g. 3-4 mm)that are drawn very tightly between the integrated circuit chip andconductive leads are typically employed. However, the need for shortlength wires drawn tightly requires relatively high tolerances, whichthereby significantly increases the complexity of fabricating thepackage.

SUMMARY OF INVENTION

It is therefore an object of the present invention to provide atechnique that allows distortion of the wire during molding whilepreventing short circuiting. It is a further object of the presentinvention to make it possible to fabricate electronic packages withoutrequiring the high tolerances associated with relatively short lengthwires drawn tightly as currently required.

It has been found pursuant to the present invention that coating thewire with a conformable dielectric material, the problem caused bydistortion during molding is eliminated. More particularly, the presentinvention is concerned with a composite that comprises an integratedcircuit chip having electrically conductive site thereon; anelectrically conductive lead; and electrically conductive wireinterconnecting the conductive site and electrically conductive lead.The wire includes a conformal coating of a dielectric thereon.

The present invention is also concerned with a method for fabricatingthe composite which includes providing an integrated circuit chip havingelectrically conductive site thereon. A conductive lead is connected tothe conductive site on the integrated circuit chip with an electricallyconductive wire. A dielectric material is then conformably coated ontothe wire. Then, the chip, wire and portion of conductive lead isencapsulated in a dielectric material.

SUMMARY OF DRAWINGS

FIG. 1 is a schematic diagram of a composite pursuant to the presentinvention.

FIG. 2 is a schematic diagram of an alternative composite pursuant tothe present invention.

BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION

Reference is made to the figures in order to facilitate an understandingof the present invention. Like numerals in different figures refer tothe same or equivalent element. In particular, FIG. 1 illustrates acomposite pursuant to the present invention wherein chip 1 is located ona chip carrier or pedestal 2. The integrated circuit chip is preferablyof silicon. The chip carrier is typically fabricated from anelectrically conductive material such as copper. It is used to create arigid mechanical system for chip/lead processing prior to molding. Ofcourse, other types of chip carriers could be used, if desired. The chipincludes electrically conductive sites 3 which are typically aluminum,gold and solder. Connected to each conductive site 3 are electricallyconductive wires 4. The wires are typically about 0.0005 to about 0.003and more typically about 0.001 to about 0.003 inches thick. Also, thewires are typically at least about 3 mm long, more typically about 5 mmlong and preferably about 5 mm to about 8 mm long. Examples of suitablewires are aluminum and gold and more typically gold. More particularly,the wire typically includes a ball like configuration at the end that isto contact the conductive site. The wire is attached to the conductivesite 3 through normal wire bonding techniques using usual bonding tools.In a preferred embodiment, the balled end of a gold wire is contactedwith an aluminum site 3 and upon the heating a eutectic is formed thatunites the aluminum site with the gold wire.

Typically, the bonding tool employed attaches the wire's other end toelectrically conductive leads 5 such as gold-coated copper leads.Although not shown in the figure, each lead 5 will have a wireconnecting it to a conductive site 3. The wire 4 is connected by heatingto typical wire bonding temperatures.

A dielectric coating 6 is then applied to wires 4. It is important tothe success of the present invention that the wires are coated withdielectric coating 6 after connection has been made between theconductive site and leads via the wire. The coating 6 is typically about0.0001 to about 0.001 inches thick and more typically about 0.0001 toabout 0.0003. The coating also typically extends over the chip 1, andends of copper leads 5. The coating must be conformable, an examplebeing a parylene coating. Parylene polymers are obtainable from UnionCarbide Corp. Suitable parylene coatings including parylene N, paryleneC and parylene D. These polymers are represented by the followingstructural formulas. ##STR1##

These polymers typically have molecular weights of about 500,000. Adiscussion of these polymers can be found in the publication entitled"Novatran Corp. Parylene Conformal Coatings Specifications andProperties, P/N 400-0001-00" by Novatran Corp., the disclosure of whichis incorporated herein by reference. The preferred parylene coatingemployed pursuant to the present invention is parylene N.

Parylene is commercially available as a dimer. Parylene N is referred toas polyparaxylylene. Parylene C is referred to asmonochloropolyparaxylylene and parylene D is dichloropolyparaxylylene.

The coating is typically applied by a vapor deposition method. Coatingapparatus such as that disclosed in "Novatran Corp. Parylene ConformalCoatings Specifications and Properties, P/N 400-0001-00"; U.S. Pat. Nos.4,401,053, 4,945,856 and WO90/02604 can be employed. A detaileddiscussion of the apparatus for carrying out the deposition is notnecessary since such can be carried out by those skilled in the artwithout undue experimentation. In a typical arrangement, the apparatusincludes a vaporizing chamber, pyrolizing chamber and depositionchamber. The parylene dimer is first vaporized at a temperature of about150° C. and pressure of about 1 Torr. Next, the dimer is pyrolyzed atthe two methylene-methylene bonds at about 680° C. and about 0.5 Torr toyield a stable monomeric diradical, such as p-xylylene. Next, themonomer enters the deposition chamber which is at about room temperatureand about 0.1 torr where it is absorbed and polymerized on the wire.

The dielectric constant of the parylene coating is typically about 3.

The composite also includes support fingers that lead from the chipsupport 2. These support fingers are typically constructed of copper.

Next, the composite is placed in a mold into which is placed adielectric encapsulating composition 8 such as an epoxy composition.Typical suitable encapsulants are disclosed in U.S. Pat. Nos. 4,235,620;4,592,944, and 4,818,812, disclosures of which are incorporated hereinby reference. The dielectric coating 6 precludes short circuiting due tomovement of the wires during this encapsulation process.

Reference to FIG. 2 illustrates an alternative embodiment of the presentinvention that further includes an electrically conductive coating 10surrounding the dielectric coating 6. Preferably, the conductive coatingis aluminum and is typically about 0.0005 to about 0.002 inches thick.Other electrically conductive materials including polymeric compositionssuch as epoxides containing electrically conductive particles can beused. This coating 10 provides for a ground that can be coupled to thechip. It is advantageous since it reduces lead inductance and givesgreater package speeds. It also provides for reduced electrical noise.In the alternative, ground can be provided by providing vias through thedielectric coating 6 to conducter 5, which in turn is electricallyconnected to a conductive pad 11. The vias can be formed by providing asuitable mask during the vapor deposition of the dielectric coating 6.

The vias are filled with the electrically conductive material 10.

In a further alternative embodiment, conducter 5 is composed of adielectric substrate such as a ceramic having electrical conductorsthereon.

What is claimed is:
 1. A method for fabricating a composite whichcomprises providing an integrated circuit chip having electricallyconductive site thereon; interconnecting conductive lead to saidconductive site with electrically conductive wire; then conformallycoating said wire with a dielectric material wherein said dielectric isparylene; then coating said dielectric material with an electricallyconductive coating and then encapsulating the chip, wire and portion ofsaid conductive lead in a dielectric encapsulating composition.
 2. Themethod of claim 1 wherein said electrically conductive site is aluminum.3. The method of claim 1 wherein said conductive lead is copper.
 4. Themethod of claim 1 wherein said conductive lead is gold-plated copper. 5.The method of claim 1 wherein said dielectric material is parylene N. 6.The method of claim 1 wherein the dielectric material is about 0.0001 toabout 0.0003 inches thick.
 7. The method of claim 1 wherein parylene iscoated on said wire by vapor deposition.
 8. The method of claim 1wherein said electrically conductive coating is aluminum.
 9. The methodof claim 1 wherein said dielectric material is about 0.0001 to about0.001 inches thick.
 10. The method of claim 1 wherein said wire is0.0005 to about 0.003 inches thick.
 11. The method of claim 1 whereinsaid wire is at least about 5 mm long.
 12. The method of claim 1 whereinsaid wire is gold wire.
 13. The method of claim 1 wherein saidencapsulating composition is an epoxy composition.
 14. The method ofclaim 1 wherein said wire is at least 3 mm long.